I finally sorted out a number of problems. I spend quite a long time reading the 749 posts on the GMECM site and that was the key. Here's the tip for the day for anyone trying to adjust Injector Constant to get the fueling roughed in. Tip: Give up on the injector constant! It doesn't do squat in the $58 code. Base fueling is determined by the BPC constants located in the BPC vs % EGR table. Recalculating the table for the 455 and 30# injectors took the constant from .089 (stock SyTy) to .124. That was the ticket! I was way lean and dorking with the injector constant in Tunercat was just leading me way down the wrong path.

Secondly,

The guy who did the swap of the IAC wires had them flipped backward. The IAC was closing up to add air.

Well at least I have an idle now. It has some surge as the IAC doesn't seem to react fast enough to stablize idle, but this could be some fueling and timing issues.

I am so freaking happy. I'll keep updating this post as I get new information.

Bort - I would be glad to contribute to your site, It surely helped me
Saturn - I'm using your base program + my fueling tweeks
Rbob- Your hints allowed me to figure out how the BPC/F28/Hex/decimal conversions work -Thank you
GM ECM site - absolutely tons of valueable information - we just need to pick through it all.


Thanks again

Steve

 

Hey thats great! The IAC problems do not surprise me as there are issues with the IAC. There doesn't seem to be a right or wrong, just will it idle or not. If not reverse them. No rhrym or rreason. (unless of course yours was really reversed lol) Thanks for the tip on the BPC. The more people that do this swap the more info we have. cheers, Bob

 

Bob,

Yea our wires were truely swapped. The postings on this board and Borts web site are correct and worked out fine. Dooooh!

Today I'll reset the base timing, Readjust the FPR, Retweek the fuel in the BPC vs % EGR (increasing the table adds fuel by the way). Rbob's calculation of BPC converted to HEX matched the HEX code in the F28 table for the stock SyTy bin file so I just back calculated everything for the 455.

Then it's off to VE table madness!

Rbob- I need to read your posts more closely from now on! I just went back and reread everything you had written and it's amazing how much I missed the first couple of times. Thanks for your help!

Also: Note to all - Just cause it shows up as a parameter to fiddle with in Tunercat or Programmer doesn't mean it's used for anything. Apparently many of these bins are a GM patch work of new and obsolete code so things aren't always as they appear.

Thanks,

Steve

 

Congrats on getting it going! That is one fine looking engine. Why is it I have this feeling that it is going to haul the groceries expeditiously .

RBob.

 

Ok here's the deal, We are definately in the ballpark with the base fueling.

but

We're really struggling with getting a stable idle. The lag time of the IAC and the fueling are giving us fits. Seems that when idle speeds up, IAC closes, then Idle goes down and overshoots, then IAC goes way open, and idle goes way high and over shoots. It's like any unstable dynamic system, it's keeps getting worse until it dies. Since our injectors and IAC are up stream from the 8:71 blower, the time lag, and accumulated fuel wetting of the blower,etc are making it very difficult to stabilize the system and O2's. We've been working with Delta IAC Enrichment and have improved things a little but we're stiill a far piece from getting a stable system. I smoothed out the closed throttle VE table and that helped some also.

Fooled with turbo transport lags but didn't see any noticeable change. Anyone know how that's supposed to work?

Increasing timing advance helped make the motor more responsive to changes but it's not enough.

Anybody have any ideas?

Thanks
Steve

 

I'm having a similar problem with my setup too. My idle is rock solid when it is cold, but then once it warms up the idle searches + or - 200 rpm. I've been playing with the IAC settings in programmer with no effect yet. I'm kind of waiting to pick up a eprom emulator from xtronics, so I can make changes and instantly see if there is an effect. I'll let you know when I get it figured out, but it will be awhile since it is cold and the Z is in winter storage.

 

look into the idle deadpan area. tweaking these adjustments will get the correction going sooner also limiting the gainword on the iac will help. might want to activate the iss tables and use some of the timing gain to help to.

 

Sorta started over. Changed cap, rotor , and plugs. Then a fresh AYBN. Set BPC to .123 and evened out the ugly Closed Throttle VE table, plus got the base timing correct. Idles much, much better now. Not perfect, but well within a range that minor tweeks to the myriad of IAC response/deadpan variables should stabilize things quite well. Haven't tried Closed Loop Idle yet. I'm sure that'l bring about a new set of challenges. Heck, even the SyTY guys complain about idle problems so I guess I shouldn't be too surprised.

Steve

 

glad to here you got it somewhere with it. playing with the iac setting will definately help you get it more stable. this will buy you time to find fuel spark issues and tune them out.

 

Did 31 burns today and have idle down to a manageable level. Now working on new problem. Just off idle about 2000 rpm and 30KPA , I have the right header glowing red. Left header looks ok. Getting a pyrometer tomorrow. Went up and down on timing, Went richer on Stoich AFR to 14.1 and had same issues. Will be checking some mechanical things tomorrow. Gonna check rocker arm adjustment on the right side. Injectors are upstream of the blower so it's hard for me to imagine a difference in fueling between the left bank and the right bank. You would think the blower would mix the AFR quite well before it hit the intake manifold.

I'll keep diggin and we'll find something.

One Q, The 749 batch fires that left and right bank separately right? Not all 8 at one time. We were looking at injector placement to try to understand the left vs right issues.

Thanks

Steve

 

fires 8 at once. as for the header glowing red id look into a fuel blockage on that side of the motor or maybe your return bypass is starving that side for pressure. also could be they way the blower discharges air. but this even with a blgockage dont make much sense with the blower the mix should be pretty homugnous. gott a pic of the insde of the intake manifold and the underside of the blower as well as the injector layout ?

 

Might be from the fuel being added above the rotors, and the centrifigal forces, and larger fuel droplets.

Too rich, and poor atomization, might take some work to get around.

If it is centrifigal forces in action you might have to settle for less then optimuim in a few spots to get things as best as possible.

2K and 30 K/Pa is an odd operating condition, IMO. Are running a different drive ratio on the blower?. Seems like an underdriven blower might do just that.

 

Started looking closer to whats going on. Looks like both headers start turning red at about the same time. (MisInformation sux). The plugs look a bit lean if anything. So, we readjusted the valves (hydraulic roller) and did about 20 more burns. Took timing to both ends of the spectrum and got no change on the glowing headers. Then I forced to run OL and started adding fuel. I added fuel up to the point we were seeing about 800MV O2. Plug cuts richened up but headers still glow. I guess is time for me to buy that wideband rather than guessing the whole way through this.

I noticed the AYBN code does not go open throttle learn enabled below 50KPA MAP. Any body know why they set this so high? It also looks like they have the O2 crossover point set to 500MV instead of 450MV. Were they trying to run the SyTY's a little richer that 14.7 in CL? I'm reading, learning, and trying not to be mislead down that slippery slope of decision making with a lack of understanding. So please, anybody reading my posts, beware that a lot of what I'm saying is observation, and conjecture. Don't take it as fact and run with it.

BTW - The blower is 1:1 driven and MAP reads about 35KPA at 2200RPM in neutral with throttle cracked open- Thats about where the headers turn to neon lights They're very pretty

Merry Xmas to all!
Steve

 

verify timing with a timing light. then get a pyrometer out or a infered gun and get the surface temps on each cylinder.i wonder if the timing is being retarded ? or more likely you could need more fuel. question which table are you adding fuel to ? if the TPS is below x % then it will use the closed throttle table. with that motor its very likely that this could be the case and that why you fuel adds arent helping at all. just a random thought. <<--- ive had trouble with this. honda tps sensors arent queit as linear as gm tps sensors.

 

Fun,

We've had the light on it and Datamaster is right on the money when you add back in the base distributor timing (which we have set at 10 deg). Don't have a good pyrometer yet. Just ordered the Aussie WB (Some how I new it was going to come down to this).

I'm with you on the TPS% and using the Closed Throttle VE table. I was there for a while also, but were up in the normal VE table and Ive been making my mass changes in the VE adder table (just for experimental purposes). This table hits both the Close Throttle VE table and the Open Throttle VE table I believe. Anyhow, I definately added fuel. BPW was up and O2 MV went from about 500 to 800.

Timing,

I guess the theory is that if timing is too far retarded, the fuel charge doesn't have enough time to burn completely in the cylinder, and finishes off the burn in the header. Sound reasonable? I'm running about 35 Deg total advance at 2200 RPM and 35KPA so its hard for me to imagine that were that far off. I definately need to find a good read on " Spark Advance 101" Anybody know of a good document?

I knew when my buddy said we were gonna get this in less that 20 burns that he was smoking something!

Happy Hoildays

Steve

 

try dropping a few degress of timing. thats a bit more then i think id like to see in that big motor. also add some more fuel in the same region. a typical 455 timming curve might work out to say 28 degress or so with a non electronic distributor. so id say emulate a factory hei curve and work from there. might explain the 800mv readings and the hot headers. well 20 bruns isnt going to happen. id say more like 200 becuase there no base bin for you to work from.

good luck and if you need fast help just email me. i answer emails faster then i respond here.